The present invention relates to a process for the preparation of an electrochemical system comprising a solid polymer electrolyte or comprising a gelled electrolyte.
Electrochemical systems for energy storage, for example batteries or supercapacitors, which operate with high cell voltages, require electrolytes which have a broad stability range. Such electrolytes are obtained by dissolution of one or more ionic compounds in a polar liquid solvent, a solvating polymer, or their mixtures. Electrochemical systems in which the electrolyte comprises a lithium salt and a polymer solvent of the polyether type are particularly advantageous. Such systems, which operate by circulation of lithium ions through an electrolyte between an anode and a cathode, can be composed of two electrodes in the form of films between which the electrolyte, also in the film form, is confined, the multilayer assembly thus formed being rolled up. However, the preparation of such a device presents problems. First, the lithium salts are generally hygroscopic and the preparation of the polyether material/lithium salt has to be carried out in an anhydrous atmosphere. Secondly, a polyether is a weakly crystalline polymer which, blended with a lithium salt, forms a complex constituting a sticky material. For this reason, it is difficult to prepare a polyether material/lithium salt film by extrusion. To overcome this disadvantage, the proposal has been made to use backing films in order to prevent the polyether/lithium salt film from sticking to itself. However, when it is desired to remove the backing film, the strong adhesion between the backing film and the electrolytic film causes splits which render the electrolyte unusable.